It's mixed driving but we live in a large city. Austin, Tx.
I updated my maintenance log sheet. For 7528 recorded miles since purchase and fuel receipts, MPG = 16.06. So the gauge is generous by 1 MPG. I have a light food compared to the wifey. I can keep the gauge above 17, she's closer to 16. When the GMIII module is out for repairs, new plugs will go in. Diff oil too. The transfer case and transmission had oil changes immediately after purchase. Maintenance and cosmetic costs so far, about 3/4 of purchase price.

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'06 X5 3.0i - bought @143,123 miles (12/26/20)